This invention relates to a semiconductor device with an improved switching characteristic.
Widely used hitherto as a switching circuit is the so-called semiconductor darlington connected circuit which comprises two transistors formed in a semiconductor wafer, one having its collector and emitter connected to the collector and base of the other, respectively. What is demanded of a switching circuit is a good switching characteristic, of course. The darlington connected circuit, however, has a poor switching characteristic. That is, its switching time is long. The poor switching characteristic of the darlington connected circuit makes a decisive defect in case the circuit is employed in a converter, inverter or switching regulator wherein a switching operation is conducted in an audible frequency band of more than 20KHz.
To improve the switching characteristic of a semiconductor darlington connected circuit, there has been invented a semiconductor device wherein a diode is connected between the base of a first transistor and the emitter of a second transistor. The diode makes the base current flow in the reverse direction when the first and second transistors are switched off. Thus the switching time period of the semiconductor device becomes shorter. The diode is generally soldered either to the electrodes formed on the semiconductor wafer of the device or to the external terminal pins of the device. During the soldering process the molten solder may flow to unnecessary areas of the semiconductor wafer surface, thereby affecting the switching characteristic of the device. Moreover, the soldering iron may scratch and damage the electrodes and wires formed on the semiconductor wafer. Further, if the diode is fitted to the external terminal pins, it needs a member which surrounds and protects it. In this case, the member helps elevate the cost of the device. Still further, the lead wire for fitting the diode has inductance, though very small (usually about 0.01.mu.H), and adversely serves to lengthen the switching time period of the device.